As a demodulation technique in digital radio communication, frequency domain equalization has been well known. In the frequency domain equalization, a frequency response of a radio transmission path is estimated by a receiver and signal distortion undergone through a transmission path is compensated, and then the signal is demodulated. Therefore, a transmission path estimation technique is required by which a frequency response of a radio transmission path can be estimated with high precision.
As a conventional transmission path estimation technique, for example, there exists a technique featuring OFDM (Orthogonal Frequency Division Multiplexing) described in Patent Document 1. In Patent Document 1, a method is disclosed in which a transmitter transmits a known pilot, signal arranged at a regular interval in a frequency domain, and a receiver 1 compares a pilot signal stored in advance with the received pilot signal so as to estimate the transmission path of the frequency domain.
Note that, since the pilot signal is transmitted at a regular interval in the frequency domain, the receiver only estimates transmission path responses of the frequencies at which the pilot signal is transmitted. Further, in the method disclosed in Patent Document 1, the IDFT (Inverse Discrete Fourier Transform) is applied to the estimated transmission path responses so as to convert them once into estimated transmission path values in a time domain, and then the estimated transmission path values are multiplied by a window function and again converted into a frequency domain signal by using the DFT (Discrete Fourier Transform) so that transmission path responses of the frequencies at which the pilot signal is not transmitted are interpolated.
Patent Document 1: Japanese Patent Publication. No. 3044899